German Patent Publication DE 32 03 961 C2 discloses an electronic transmitting-receiving switch for a transceiver, wherein the switch uses current-controlled diodes. Transceivers equipped with such switch-over devices reduce the level of a very powerful radio frequency reception signal in the first radio frequency amplifier stage of the receiver. An attenuator required for this purpose uses pin diodes which, above a predefined radio frequency level, e.g 1 MHz, form an essentially ohmic resistor for the radio frequency. The ohmic resistor is adjustable by means of a direct current flowing through the pin diode. If no direct current flows through the pin diode, the pin diode will be a high ohmic resistance for the radio frequency. Instead of using pin diodes it is possible to use GaAs field effect transistors for such attenuators.
A radio frequency diode switch, intended for use as a transmitting-receiving switch-over device, is also known from a leaflet by muRata, Multilayer Component Dept., New Business Development Division, publication no. LMX-PR-014, dated June 1994. This switch-over device features two diodes and two quarter-wave (.lambda./4) conductor sections. Radio frequency terminals are provided for the transmitter, the receiver, and the antenna. In addition there are two control terminals to which the voltages +5 volts and 0 volts are applied for transmitting, and the voltages 0 volts and +5 volts are applied for receiving. A direct current flows through both diodes during transmission for making the path from the transmitter to the antenna conductive while RF-shorting the receiver input. However, when the other polarity of the voltage is applied to the control terminal of both diodes the transmitting path is blocked and the radio frequency thus can only get from the antenna terminal to the receiver.
It is also known to lower the receiving level within the area of the first receiver stage, to use a dual gate MOS FET instead of a pin diode specifically provided for this purpose. The control signal is applied to gate 2 of the dual gate MOS FET. Other known possibilities relate to using a GaAs FET with a gate voltage control, or a transistor with an operating point adjustment, or even to switch off or over one or several transistor stages, e.g. by RF relays (two stage control). Particular effort and expenditure are required for these several possibilities.
The known solutions have the disadvantage that they require at least one additional circuit involving related costs and space requirements. Problems may also occur with intermodulation and cross-modulation. The additional electronic components contribute additional electronic noise. For achieving a more favorable intermodulation and cross-modulation characteristic, only the above-mentioned two-stage control device is possible among the known possibilities.